In quilting machines of various types, threads are applied and manipulated on opposite sides of a fabric to form one or more patterns of stitches. The proper formation of the stitches of each series requires the movement and precise timing of cooperating stitching elements. Some quilts are stitched with continuous patterns along webs of material that is later cut, without the need to start and stop the quilting of a pattern in the midst of a quilted product. Many standard mattress covers are quilted on multi-needle quilting machines in this manner. Other patterns start and stop on a quilted product, which might include a number of discrete disconnected pattern components on a given quilted product. Multi-needle quilting machines can quilt mattress covers in this manner, as described in commonly assigned U.S. Pat. Nos. 5,154,130 and 5,544,599, hereby expressly incorporated herein by reference. Comforters and certain more expensive mattress covers are quilted as single panels on single needle quilting machines in this manner, as described in commonly assigned U.S. Pat. Nos. 5,650,916, 5,685,250 and 5,832,849, hereby expressly incorporated by reference herein. When a pattern starts or stops on a product, at the end of the stitching of a pattern, a tack is usually sewn, thread is cut, and the relative position of the fabric and the stitching elements is changed to sew another stitched pattern on the same or on another product.
Multi-needle quilting machines and some single needle quilting machines for quilting mattress covers and other quilted products having only one outer finished side use a double lock chain stitch. The chain stitch is formed by poking loops of a bottom thread through loops of a top thread, and can be employed using large spools of top and bottom threads, but because the loops are visible on the underside of the product, one side of the product is unattractive. Single needle machines and some multi-needle machines for quilting comforters and mattress covers and other products use a lock stitch. The lock stitch is formed by passing the bottom thread once through each loop of the top thread, which, by taking up the top thread loop so that the thread crossings are essentially within the quilted material, produces a line of stitches that appear the same from both sides. Forming of a lock stitch requires passing the entire bottom thread supply through each top thread loop. As a result, lock stitch machine use small quantities of thread would on a bobbin so that the top thread loop can be hooked and rotated around the bobbin and hence the single strand of bottom thread.
Many lock stitch quilting machines have a common structure in which a reciprocating needle is mechanically coupled to an upper sewing head motor located above a layered fabric. The needle reciprocates through layered fabric and through a needle plate supporting the layered fabric. With a lockstitch quilting machine, a lower sewing head includes a hook drive that is mechanically coupled to a bobbin case containing a spool of thread. The lower sewing head may be linked to and driven by the needle drive motor or by the hook drive motor, synchronized to the needle motion, to move the hook drive around the bobbin case to pick up thread from the spool in synchronization with the motion of the needle and thread below the layered fabric. The thread from the reciprocating needle and the thread from the bobbin case form a lockstitch securing the layers of fabric together in a known manner.
The nature of the lockstitch requires that the bobbin thread be reduced to a minimum size in order to allow the thread from the needle to be rotated about the bobbin case thread to form the stitch. The limited size of the bobbin case limits the quantity of thread that can be stored within the bobbin case. Usually, in commercial lockstitch quilting, some scheme is used to alert a machine operator when there is insufficient thread left on the bobbin to quilt a complete quilted product, so that the operator can change bobbins manually before starting a product. Otherwise, it is necessary for the operator to manually operate the machine to cut thread, tack the stitches if necessary, and change bobbins in the middle of a quilted patter.
When quilting larger workpieces, for example mattress covers, a particular stitch pattern may require more thread than can be stored in a common, commercially available bobbin case. Therefore, the thread spool and bobbin case would have to be changed in the middle of a workpiece quilting cycle. An manual operation to change a bobbin, particularly in the middle of the quilting of a pattern, requires that a machine operator stop the operation of the upper and lower sewing head motors, manually command the quilting machine to move the sewing heads to a maintenance position and remove the bobbin case with the empty thread spool. Thereafter, the machine operator must install a bobbin case with a full thread spool, command the quilting machine to move the sewing heads back to the position where the bobbin thread ran out and reinitiate the stitching cycle. Such a bobbin case changing operation is labor intensive, time consuming, inefficient, extends the time required for part production and thus, adds significant cost to the production of the workpiece.
Therefore, there is a need to provide apparatus and methods for automatically changing a bobbin case on a quilting machine, thereby substantially improving its efficiency.